1. Field of the Invention
The present invention relates to a zoom lens and an imaging apparatus using the same and, more particularly, to a zoom lens having an optical system whose optical axis is bent and an imaging apparatus using the same.
2. Description of the Related Art
In recent years, digital cameras (electronic cameras) have received attention as the coming generation of cameras, an alternative to silver-halide 35 mm-film (usually called 135 format) cameras, and are now available in a wide spectrum of categories from commercial high-end to portable low-end types.
In view of the category of the portable low-end type in particular, the primary object of the present invention is to provide the technology for implementing, at low cost, video or digital cameras whose depth dimension is reduced while high image quality is ensured, easy to handle, and have a high zoom ratio capable of covering a wide focusing distance range from the wide-angle end to the telephoto end.
The greatest bottleneck in thinning down cameras in their depths direction is the thickness of the surface of an optical system, especially a zoom lens system, located nearest to its object side to an image pickup plane. The technology currently in vogue for thinning down camera bodies is the adoption of a collapsible lens barrel that allows an optical system protrudes from the front side of the camera body in photography and incorporated in the camera body when the camera is not used.
The adoption of the collapsible lens barrel, however, requires much time to bring lenses into a working state from an incorporating state, which is unfavorable for use. Furthermore, the design that the most object-side lens group is moved is unfavorable for water and dust proof. In recent years, in order to obtain a camera which does not have rising time (lens shifting time) required to bring the camera into the working state like the collapsible lens barrel, is favorable for water and dust proof, and is extremely small in depth, it is conceivable that the optical system is constructed so that the optical path (optical axis) is bent by a reflective optical component such as a mirror or prism. In the optical system used, the lens group nearest to the object side remains fixed in position, with a reflecting optical element located therein. An optical path portion following that lens group is bent in the longitudinal or transverse direction of a camera body, so that its depth dimension can be minimized.
In addition, in portable low-end type video and digital cameras on which the present invention has focused attention, ones having a half field angle of about 30° at the wide-angle end are mainstream. However, wide-angle video and digital cameras having a further enlarged photographing area are now expected.
As examples of a wide angle zoom lens adopting a bent optical system, there is known one disclosed in Patent Documents 1 and 2. However, a zoom lens of Patent Document 1 (JP-A-2004-354871) has a half field angle as large as about 37° while the zoom ratio thereof is not much more than about 2.8. Although a zoom lens of Patent Document 2 (JP-A-2004-354869) has a half field angle as large as about 37° and zoom ratio thereof is as large as about 3.7, the entire length of the zoom lens is long.